Merge branch 'js/rebase-deprecate-preserve-merges'

"git rebase --rebase-merges" replaces its old "--preserve-merges"
option; the latter is now marked as deprecated.

* js/rebase-deprecate-preserve-merges:
rebase: deprecate --preserve-merges

diff --cc Documentation/git-rebase.txt
Simple merge

diff --cc builtin/rebase.c
Simple merge